Determination of the quadrupole coupling constant from a featureless NMR lineshape
Five spin-locking sequences (Y-X, SL1, SL2, SL3, and SL4) with various phase cyclings are presented in this applet. In the following pulse sequences, the RF phases are indicated in curly brackets, and acq(+y) means the FID is detected in the +y-axis of the receiver with quadrature phase.
The left part of the simulation panel indicates the physical parameters which are preset for a typical experiment on a spin I = 3/2 in a powder. You can introduce your own values.
First, we select one of the spin-locking sequences with the upper choice box.
Then, we select the type of line intensity calculation available
with the lower choice box:
(1) V-V: p1 and p2 vary simultaneously;
(2) V-F: p1 is variable and p2 is constant;
(3) F-V: p1 is constant and p2 is variable.
For V-V case, only the parameters for p1 are required.
For V-F and F-V cases, the constant pulse-length should be provided in the MinLength field.
MinLength: the first variable pulse-length in µs
MaxLength: the last variable pulse-length in µs
Step: the increment of the variable pulse-length in µs
Depending on the spin-locking sequence used, the FID of the central transition is detected in one of the two channels in quadrature of the receiver. Therefore, after pressing the RUN button in the right part of the simulation panel (not shown), we use the check buttons to choose the real or the imaginary parts of the line intensity. In contrast, the satellite-transition signals are detected in both channels of the receiver.
As the rotary-echo sequences, these spin-locking sequences cancel signal with small or large quadrupolar coupling constants. Furthermore, the SL4 sequence also cancels the spurious signals as the composite-pulse sequence does.
The following applet is initialized for the central-line intensity of a spin I = 3/2 in a powder excited by the basic Y-X spin-locking sequence where p1 and p2 vary simultaneously from 0 to 10 µs by 0.5 µs step. The experimental line intensities are identical to the simulated ones.
JDK1.0.2 applet for spin-lock nutation sequence applied to a powder